This invention relates generally to the separation of components from a feed stream through the use of adsorption and desorption and more particularly to the provision of such a process wherein desorption is carried out in multiple steps at different temperatures to improve the separation of the components.
Adsorption has been used to remove small amounts of impurities or small quantities of valuable products from liquids or gases and to remove and recover solvents from air used in solvent drying. Adsorption has been proposed, but not extensively used for high volume products primarily because the use of solids makes it more difficult and complex to use continuous processes and multiple stages. Unless an almost complete separation can be obtained in one stage, adsorption is often an unfavorable process.
In a typical adsorption-desorption separation process, a feed stream of the mixture is charged to the inlet of a fixed bed of adsorbent material which preferentially adsorbs one of the components of the mixture that is present, usually a component with a small concentration. The feed stream passes through the bed and the effluent is withdrawn from the outlet of the bed, the effluent having a decreased content of those components that have been adsorbed by the bed. The process continues until the adsorbent is substantially saturated and then, the bed is regenerated.
A method of previously employed to regenerate the bed comprises passing hot regeneration gases through the bed of adsorbent material, either in the direction of flow of the feed, or in the opposite direction of the feed. See, e.g., Hengstebeck, U.S. Pat. No. 3,080,433. Alternatively, desorption has been carried out in one step by lowering the pressure, by passing a gas or vapor containing a minimum of the adsorbed components over the bed of absorbent, by heating to a high temperature, or by a combination of these methods.
Where desorption is carried out in one step, and more than one component is adsorbed, all of the adsorbed components are removed together. Accordingly, the desorbed material has the same amounts of each component as existed in the adsorbed state on the adsorbent and the desired separation may not be obtained with one step of desorption. However, if desorption could be carried out in multiple steps, with one or more of the adsorbed components being preferentially desorbed in a first step and one or more of the remaining adsorbed components preferentially desorbed in a subsequent step, greater separation could be achieved. Such further separation would clearly increase the economies of adsorption as a means for separation.